Electric rectifier control grid



May 15, 1933. w. BovERl ET AL 1,908,949

ELECTRIC RECTIFIER CONTROL GRID Filed May 16, 1931 l i l i l l 7 /4 /4/Z /8 v/Z ,g mm- /9 /nyen/ors l/I/f//i Bove/v Patented May 16, 1933UNITED STATES lParent oFFicE VJ'ILLI BOVERI, OF ZURECB, AND RMINLEUTI-IOLD, OE' vBADEN,4 SWTZERLAND,

ASSIGNORS TO AKTIEN GESELLSCHAFT BROWN BOVERI & GE., OF BADEN, SWITZER-LAND, A JOINT STOCK COMPANY OF vSW'I'IZERIILAND Y ELECTRIC RECT'IFIERCONTROL GRIDl Application filed May 16, 1931, Serial No. 537,832, and inGermany May 26, 1930.

This invent-ion relates to improvements in grid arrangements for theanodes of electric power rectiiers of the metallic vapor arc type inwhich the grids are utilized to control the operation of the rectifierby controllingA the time of attachment of the arc on the anodes. Y

Constructions in the form of screens, sieves, sleeves or the like haveheretofore been inserted in the tank ooi-tion surrounding the anodes orin the arc guides arranged about the anodes of electric powerrectifiers. Such constructions were arranged in either insulated oruninsulated relation with the surrounding tank portion or arc guides andfrequently had a negative potential impressed thereon to make the arccontrollable by controlling the time of attachment of the are on theanodes. rllhe negative potential increases the voltage required for theignition of the arc on the controlled anode so that its ignition isdelayed and re-ignition, and therefore backliring, of the anode isprevented. The same result may likewise be attained by the aid of gridswhich do not have a negative potential impressed thereon if the gridsare so arranged adjacent the anodes that they are surrounded on allsides by the arc flowing from the anodes. Such arrangement ofuncontrolled grids permits the extraction thereby of heat from the arcor the grids may be heated from an exterior source. Such heating causesthe surrounding metallic vapor to be superheated thereby decreasing thevapor density, pre-4 vents the access of unvapoized cathode material tothe anodes and also prevents the condensation of residual gases on theanodes. ldacklires due to the formation of cathode spots on the anodesare thus prevented.

Constructions have also been proposed in which bot-h controlled anduncontrolled grids, i. e. grids having and not having a negativepotential impressed thereon, are arranged over each other across thelongitudinal axis of the arc guides. that all of the above gridarrangements are not sul'licient to control the arc in many cases. Suchfailure is due to the fact that the negatively charged grid itself emitscharge carriers from its surface into a layer of ions formed thereabout.A wandering of the Research has shown however Y charge carriersfrom thegrid to the anode thus takes place even though the grid openings may bemade small enough so that they are completely filled by the layer ofions. In

the use of gridswith such small openings, i

however, great care must be taken that the openings are not soexcessively restricted as to hinder the passage of the arc therethroughafter the archas been ignited. In addition to the above effect, surgeionizations due to the vapor density also occur in the space between thegridsand the anodes, which ionizations canse automatic discharges sothat the layer of ions about the grids is destroyed and a grid controlof the arc is impossible.

lt is, therefore, among the objects of the present invention to providea grid structure to be enclosed within the tank portion of an electricpower rectier of the metallic vapor are type immediately surrounding theanodes in which both the heating effect of uncontrolled grids and therepulsive effect of controlled grids are used to control the moment ofattachment of the arc.

Another object of the invention is to provide a grid structure to beenclosed within the arc guides about the anodes of an electric powerrectifier of the metallic vapor arc type in which a grid which is notsupplied with a potential is arranged to ext-ractheatfrom the arc todecrease the vapor Adensity adjac-ent the anode and a grid having apotential supplied thereto is used to control the movement of theelectric charge carriers.

Another object of the invention is to provide a grid structure to beenclosed within the arc guides about the anodes of an electric powerrectifier of the metallic vapor arc type in which an uncontrolled gridis arranged between a controlled grid and the anodes.

Objects and advantages, other than those above set forth, will beapparent fromthe following description when read in connectionwith theaccompanying drawing in which Figure l invention in verticalcross-section in which' an uncontrolled grid is arranged between acontrolled grid, within the arc guide, and an anode, and l y e5illustrates one embodiment of the i Y F ig. 2 is a fragmentary viewsimilar to that shown in F ig. 1 but showing a modifi-ed form of thestructure of the uncontrolled grid.

Referring more particularly to the drawing by characters ofreference,vthe reference numeral 6 designates an anode extending throughthe cover 7 of a metallic rectilier tank (not shown) through aninsulator' 8. An arc guide 9, suspended from the insulator 8 and havingan open lower end, partial'- ly encloses the anode 6 andegtends toward acathode (not shown) of vaporizable metal retained in the tank asis usualin electric power rectiiier of the metallic vapor arc type. l

1 A gridll, here shown as being formed of short cylinders'of currentconductive material arranged in concentric space relation with thesurfaces thereof parallel with the surfaces of thearc guide 9, issupported a short distance below the lowermost surfaces of the anode '6on insulators 12. The grid 11 may also be made in the form of a screenor sieve arranged across the arc guide if desired. The grid isYconnected with a suitable source of control potential (not shown) bymeans of conductors 13 passing 'through bushings 14 in the arc guide 9.l A grid 16, here shown as formed of short cylinders of heatresistivematerial arranged in concentric relation with the walls of the arcguide, is supported by suitable bolts 17 which may b-e insulated fromthe arc guide, between the controlled grid 11 and the lower surfaces ofthe anode 6. The grid 16 is not controlled i. e. is not connected with asource of potential. A screen or sieve may also be used in place of theconcentric cylinders to form the uncontrolled grid 16 in which case thespace between the controlled grid l1 and the anode 6 is very small whichis advantageous.

The grid 16, being directly ahead of the anode in the direction of iiowof the are therefrom, is very highlyheated by the arc and the spaceabout the grid, and hence about the anode, is very highly overheated sothat the metallic vapor density in Y'such space is very low. To aid inthe result produced by heating of the grid 16, the grid may also beheated by an external source of heat. The charge carriers emitted fromthe lanode itself, or produced from the layer of ions about the grid orby the control grid 11 when the arc is not completely blocked thereby,are then entirely taken up by the uncontrolled grid V16. Theoccurrenf'zey of automatic discharges or surge ionizations between thecontrolled grid and the anode is thus avoided by the overheateduncontrolled grid in the space ofthe lowest vapor density and the lowestdensity Vof the charge carriers.

lA second uncontrolled grid 18, formed as a screen, is supported, bysuitable boltsl as at 1.9, below the controlled grid 11. The grid 18 maybe connected with an exterior source of heat and the two uncontrolledgrids 16 and 18 may be conductively connected. The

second uncontrolled grid 18 prevents the acinders forming the controlledgrid 11.

The grid arrangement disclosed by the present invention also provides animportant protection against backiring during normal operation of therectifier for the reason that the anodes are more readily controllableby the formation of a Zone of low vapor density and low mass of chargecarriers directly ahead of the lowermost surfaces of the anodes. A zoneof the highest impenetrability is thus formed at the location at whichautomatic discharges usually cause the appearance of backires. Such zonemakes the oc"- currence of an automatic discharge-or surge ionizationimpossible.

Although but two embodiments of the present invention have beenillustrated and described, it will be apparent to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the spirit of the invent-ion or from the scope of theappended claims.

yThe invention claimed is:

1. Means for controlling the attachment of the arc to the anodes of anelectric power rectifier of the metallic vapor arc type comprising agrid to be controlled by the supply of a potential thereto, and anuncontrolled grid, said grids being arranged in the path of the arcflowing from the anode, and the said uncontrolled grid being arrangedbetweensaid anode and said to be controlled gri 2. Means for controllingthe attachment of the arc to the anodes of an electric power rectifierof the metallic vapor arc type, the anodes being partially enclosed byarc guides, the means comprising a grid to be controlled by the supplyof a potential thereto, and Van uncontrolled grid, said grids beingarranged within the arc guides ahead of the anodes in the direction offlow of the arc therefrom.

3. Means for controlling the attachment of the arc to the anodes of anelectric power rectifier of the metallic vapor arc type comprising agrid to be controlled by the supply of a potential thereto, and aplurality of uncontrolled grids, -said grids being arranged in the pathof the arc flowing fromthe anodes, rone of the uncontrolled lgrids beingarranged between the anode and said `to be vcontrolled grid.

by the supply of a potential thereto, insulating means supporting saidto be controlled grid ywithin the arc guide, and an rincontrolled grid,conductive means supporting said uncontrolled grid within the arc gulde,said grids being arranged withinv the arc guide ahead of the anodes inthe direction of flow of the arc therefrom.

5. Means for controlling the attachment of the arc to the anodes of anelectric power Y rectifier of the metallic Vapor arc type, the anodesbeing partially enclosed by arc guides, the means comprising a grid to be controlled by the supply of a potential thereto, and an uncontrolledgrid, said grids being arranged within the arc guide ahead of the anodein the direction of flow of the arc therefrom, and the said to becontrolled grid being arranged between said uncontrolled grid within theare guide.

6. Means for controlling the attachment of the arc to the anodes or" anelectric power rectilier of the metallic vapor arc type, the anodesbeing partially enclosed by arc guides,

the means comprising a grid to be controlledl by the supply of apotential thereto, and an uncontrolled grid, said grids being arrangedin the path of the arc l-owing from the anode and being formed of spacedconcentric cylinders exten ding parallel with the arc guides.

7. Means for controlling the attachment of the arc to the anodes of anelectric power rectifier of the rmetallic Vapor arc type, the anodesbeing partially enclosed by arc guides,

the means comprising a grid to be controlledv by the supply of apotential therto, and an uncontrolled grid, said grids being arranged inthe path of the arc flowing from the anode and being formed of spacedconcentric cylinders extending parallel with the arc guides, thecylinders of said ,grids being arranged in interleaved relation.

8. Means for controlling the attachment of the arc to the anodes of anelectric power rectifier of the metallic Vapor arc type, the anodesbeing partially enclosed by arc guides, means comprising a grid to becontrolled by the supply of `a potential thereto, and a plurality ofuncontrolled grids, said grids being arranged in the path of the arcflowing from the anode, one of said uncontrolled grids be- ;tormed ofspaced concentric cylinders extending parallel with the arc guide, andthe other of said uncontrolled grids being formed as a screen extendingacross the arc guide.

In testimony whereo we have hereunto subscribed our names this 29th dayof April WILLI BOVERI. ARMIN LEUTHOLD.

DISCLAIM ER 1,908,949-Willi Boverfi, Zurich, and Armin Leuthold, Baden,Switzerland. ELEC- TRIO RECTIFIER CONTROL GRID. Patent dated May 16,1933. Disclaimer ledO September 30, 1939, by the assignee,Aktiengesellschaft Brown Boveri & ie. Hereby enters this disclaimer toclaims 2 and 4 of said Letters Patent.

[Oficial Gazette October 24, 1.939.]

